Electromagnet with permanent magnet held by a cage

Abstract

A pole piece (14a) of the movable core (12) moves in an air gap (25a) between external (61) and internal (16) pole pieces. A pole flange (14b) of the same core (12) moves in an air gap (25b) between a portion (30b) of the external pole piece (61) and a magnetic lobe (36) which is in contact with this latter. A permanent return magnet (17) is disposed between the internal (16) and external (61) pole pieces. The magnet (17), the internal pole piece (16) and the lobe (36) are maintained in a cage (60) of plastic material snap fastened by hooks (78, 80) on the external pole piece (61). Three cross pieces (75, 76, 77) connecting two longitudinal walls of the cage to each other, suitably separate the different magnetic components. The force of attraction of the magnet (17) prevents the pole pieces (16, 61) from leaving it.

We claim: 
     
       1. Electromagnet comprising an induction winding and first and second magnetic devices movable relative to each other, the first device comprising a core surrounded by the winding, the second device comprising an internal pole piece, relatively close to the winding and an external pole piece relatively far from the winding, a permanent magnet interposed between the external and internal pole pieces, the core bearing on at least one side of the winding a pole flange disposed in an air gap which is defined between the internal and external pole pieces, wherein an amagnetic cage is snap fastened on the external pole piece and comprises for the permanent magnet and for the internal pole piece respective recesses defined by means for positioning and retention with respect to displacements transverse to the magnetic axis of the permanent magnet. 
     
     
       2. Electromagnet according to claim 1, wherein as snap fastening means the cage comprises hooks engaged in recesses in the external pole piece. 
     
     
       3. Electromagnet according to claim 1, wherein the cage comprises two longitudinal walls between which the pole pieces and the permanent magnet are stacked. 
     
     
       4. Electromagnet according to claim 3, characterized in that each longitudinal wall has a recess in which is engaged an ear of the internal pole piece. 
     
     
       5. Electromagnet according to claim 1, wherein the cage comprises two cross pieces disposed between the pole pieces on opposite sides of the permanent magnet and locating the latter. 
     
     
       6. Electromagnet according to claim 1, wherein as to displacements parallel to the magnetic axis of the permanent magnet, the pole pieces and the permanent magnet are immobilized by the force of the permanent magnet. 
     
     
       7. Electromagnet according to claim 1, wherein on the side of the air gap, the cage has two flanges extending toward each other, which position the internal pole piece relative to displacements in a direction of narrowing of the air gap. 
     
     
       8. Electromagnet according to claim 1, wherein on the side of the internal pole piece remote from the air gap, the cage defines a recess for a magnetic lobe which is in magnetic contact with the external pole piece and which defines with the transverse region of the external pole piece an air gap in which there is relative mobility of a second pole flange of the core and of the external pole piece, between a position in which the second pole flange bears against the external pole piece and a position in which the second pole flange is adjacent the lobe. 
     
     
       9. Electromagnet according to claim 8, wherein the cage comprises a partition wall disposed between the lobe on the one hand and the magnet and the internal pole piece on the other hand. 
     
     
       10. Electromagnet according to claim 8, wherein the cage comprises snap fastening means maintaining the lobe in bearing contact against the external pole piece. 
     
     
       11. Electromagnet according to claim 8, wherein the induction winding comprises winding turns formed between two winding end flanges, and wherein the cage maintains the lobe such that its air gap face is substantially in the plane of one of the winding end flanges, and maintains the internal pole piece such that its air gap face is substantially in the plane of the other winding end flange. 
     
     
       12. Electromagnet according to claim 1, wherein the cage is of plastic material.